Borehole cleaning apparatus and method

ABSTRACT

Oilfield cleaning apparatus is provided for cleaning the inner wall of an oilfield tubular. The apparatus comprises a body to be introduced into the tubular, the body being provided with annular cleaning elements. Furthermore a rotary drive acts to oscillate the cleaning elements in contact with the inner wall of the tubular to scrape debris from the inner wall with the cleaning element. Each cleaning element is mounted on a rotary bearing member which is inclined relative to its axis of rotation so as to cause the cleaning element to be oscillated axially in contact with the inner wall as the bearing member is rotated, Also a catcher tube is provided to catch the heavier debris which is not washed away by the flow of fluid up the borehole. Such apparatus provides an active cleaning action which is particularly effective in removing deposits from the inner wall of the tubular.

BACKGROUND OF THE INVENTION

This invention relates to an oilfield cleaning apparatus and a methodfor cleaning the inner wall of an oilfield tubular. Such apparatus canbe used for cleaning casing or pipeline tubulars in the petroleumindustry, either downhole or when used on the surface or subsea for thetransmission of oil or gas.

When running casing into a borehole in the construction of oil and gaswells, cement is commonly used to seal the casing into the hole and toseal between casings. This cement leaves scale residues in areas on thecasing where it is not required, and cleaning tools must be used toremove such residues.

Furthermore oil or gas is prone to produce scale deposits, such asbarium sulphate and calcium carbonate, on the inner walls of productiontubing, and such scale deposits must also be removed using cleaningtools from time to time to prevent restriction of production rates.

Additionally oil produced from oil wells may in some cases carry highlevels of wax which, as the oil cools, itself produces deposits alongproduction flow lines. These deposits are also a form of scale whichmust be removed by use of cleaning tools if the oil transmission rate isto be maintained. In some cases, water produced with the oil carrieswith it minerals, such as calcium and barium, which can also bedeposited in layers on the inner walls of production flow lines,together with the wax, to create laminated scales which can be verydifficult to remove.

In all the above cases, it is necessary to use cleaning tools and/orchemical solvents to remove the unwanted deposits. However themechanisms and cleaning tools used to remove the various scalesencountered in the petroleum industry have not changed significantly formany years. In the case of cement scales, the mechanical scrapers orfixed brushes employed have to be moved up and down the tubular toproduce the required cleaning action. An example of a prior referencedisclosing such a cleaning tool is U.S. Pat. No. 4,896,720. Furthermoremilling has been employed to remove the harder scales, such as bariumsulphate and calcium carbonate. In addition chemical solvents have beenused in isolation and together with mechanical removal systems, withvarying degrees of success. In production pipelines, cleaning pigs areusually used in association with solvents, but this is an expensiveexercise which needs to be repeated many times for effective cleaning.

It is an object of the invention to provide an improved technique forcleaning oilfield tubulars, such as pipe and casing sections, in suchapplications.

BRIEF SUMMARY OF THE INVENTION

According to the present invention there is provided oilfield cleaningapparatus for cleaning the inner wall of an oilfield tubular, theapparatus comprising a body to be introduced into the tubular, the bodybeing provided with at least one cleaning element, and drive meansacting to oscillate the cleaning element in contact with the inner wallof the tubular to scrape the inner wall with the cleaning element.

Such apparatus obviates the shortcomings of the prior art in that itprovides an active cleaning action, which can be rotary, motor orturbine driven, utilising one or more oscillating cleaning elements. Thecleaning elements can be grouped in modules on a common drive shaft, andthe drive shaft can be used to drive an impeller which guides heavydebris not circulated out of the tubular to be drawn into a catcherelement.

The invention also provides a method of cleaning an inner wall of anoilfield tubular, the method comprising introducing into the tubular abody provided with at least one cleaning element so that the cleaningelement contacts the inner wall of the tubular, and operating a drive tooscillate the cleaning element to scrape the inner wall with thecleaning element.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more fully understood, preferredembodiments of apparatus in accordance with the invention will now bedescribed, by way of example, with reference to the accompanyingdrawings, in which:

FIG. 1 is a cut-away view of a first embodiment of the invention withina borehole;

FIGS. 2 and 3 are explanatory diagrams showing details of the firstembodiment;

FIG. 4 shows a lower section of the first embodiment illustrating theflow paths;

FIG. 5 is a side view of part of a second embodiment in accordance withthe invention;

FIG. 6 is a perspective view of a detail of the second embodiment; and

FIG. 7 is a perspective view of part of a third embodiment.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a downhole cleaning tool 1 introduced into a casing 2within a borehole for removing deposits from the inner wall 3 of thecasing 2. The tool 1 comprises a body 4 in the form of a section ofdrill pipe located at the end of a pipe string to be rotated from thesurface in conventional manner. At the same time as the pipe string isrotated in the direction of the arrow 5 fluid in the form of drillingmud is circulated down the pipe string in the direction of the arrow 6 aso as to pass along an axial passage through the body 4 and back up theannular space 6 a between the body 4 and the inner wall 3 of the casing2.

The body 4 incorporates a hollow hub 7, and four annular cleaning units8 are mounted on the hub 7 by means of rotary bearings 9, as will beappreciated by referring to the explanatory diagrams of FIGS. 2 and 3showing the mounting of one such cleaning unit 8 from the side and inaxial section respectively. Each cleaning unit 8 is provided withcleaning elements in the form of pads of outwardly extending bristles 10equiangularly distributed around the circumference of the unit 8. Gaps11 are provided between the pads for flow of fluid. Each cleaning unit 8may have an outer surface 8 a (as shown in FIG. 1)which is curved in theaxial direction to assist contact with the inner wall 3 during thecleaning action. As best seen in FIG. 3, each cleaning unit 8 is mountedby its associated bearing 9 such that its central axis 12 a is inclinedrelative to the axis of rotation 13 of the bearing 9, so as to cause thebristles 10 to be oscillated axially in contact with the inner wall 3 ofthe casing 2 as the hub 7 is rotated. Furthermore the cleaning unit 8may be offset axially (upwardly in FIG. 3) from the centre line of thebearing 9 so that the bristles 10 are movable towards and away from theinner wall 3 by rotation of the hub 7. Although the cleaning unit 8 ismounted on the hub 7 by the rotary bearing 9, the fact that the bristles10 are in engagement with the inner wall 3 during cleaning means that,as the hub 7 is rotated, the bristles 10 rotate to only a limited extentwith the hub 7. However the rotary movement of the hub 7 causes thebristles 10 to move inwardly and outwardly and upwardly and downwardlyrelative to the inner wall 3 to impart the required scraping action.

Thus, on rotation of the pipe string, the cleaning units 8 are caused tooscillate with diametrically opposite portions of the cleaning units 8oscillating in opposite directions and corresponding portions ofadjacent units 8 also oscillating in opposite directions to one another,to scour the deposits from the inner wall 3. At the same time fluid iscirculated from within the body 4 through rotating jet nozzles 12extending through the hub 7 at locations intermediate the cleaning units8. The jets of fluid emitted by the nozzles 12 serve not only todislodge deposits from the inner wall 3 but also to dislodge depositsattached to the bristles 10 of the cleaning units 8.

Most of the dislodged debris is circulated away in the fluid flow whichtravels up the annular space 6 a between the pipe and the inner wall 3.However heavy particles, which are not circulated out of the borehole,are guided into a catcher tube 14 which is attached to the bottom of thebody 4 by a rotary bearing 15 and which is prevented from rotating toany substantial extent during rotation of the pipe string by beingprovided with drag springs 16 which engage the inner wall 3 of thecasing 2.

In order to guide the heavy debris into the catcher tube 14, rubberwiper cups 17 are provided in the annular space surrounding the top ofthe catcher tube 14, and a suction impeller screw 18 is provided on thebody 4 within the top of the catcher tube 14, the impeller screw 18being caused to rotate with the body 4 so as to draw fluid entrainingthe debris into the catcher tube 14 towards a debris containment area 19at the bottom of the catcher tube 14. The fluid entering the catchertube 14 is allowed to escape by way of angle ports 20 provided in theside wall of the tube 14 and arranged so that the heavy particulatematter is retained within the containment area 19 for later recovery tothe surface. In a possible modification, stabiliser fins or gauge padsmay be provided on the catcher tube 14 for engaging the inner wall 3 ofthe casing 2.

In this way the apparatus provides an effective brushing and recoverysystem for the cleaning and removal of scale from casing and tubing. Itshould be noted that the apparatus described above could also be run oncoiled tubing by the inclusion of a downhole motor to provide rotationaldrive to the body 4. In this case circulating and jetting fluid would beprovided by exhaust from the downhole motor.

Various modifications of the above described apparatus may beincorporated to suit different applications. For example FIG. 5 shows atool having a body 21 provided with a top connector 22 and a bottomconnector 23 for connection to pipe sections within a pipe string towhich rotary motion is imparted in a manner already described. In thiscase annular cleaning units 28 are mounted on a hub 27 incorporatingjetting nozzles 12 in a similar manner to the cleaning units 8 alreadydescribed above. However the cleaning units 28 differ from the cleaningunits 8, as best seen in FIG. 6, in that they are provided with rigidmetal studs 29 for engaging the inner wall of the casing while beingoscillated axially in use by rotation of the body 21.

It should be appreciated that both the cleaning units 8 and the cleaningunits 28 are readily detachable from the tool for replacement by newcleaning units which may be of a different type, for example of a fineror coarser brush configuration, or of the same type to the originalcleaning units. Various types of cleaning unit are contemplated withinthe scope of the invention, and these include bristles and studs ofvarious densities and configurations, possibly encapsulated in a rubbermatrix as described in published International Application No. WO98/06927.

In a further embodiment the tool may incorporate one or more tractorsections 30 as shown in FIG. 7 for moving the tool along the borehole.For example cleaning units 8 or 28 as described above may be provided inmodules mounted between intermediate tractor sections to provide a toolwhich may be moved along the borehole in a moving fluid stream obtainingits motive power from the moving fluid, the cleaning modules beingprovided for the removal of wax and scale in subsea pipelines, forexample. Such tractor sections may be constructed generally as describedin International Application No. PCT/GB00/02053, and a number of suchsections may be articulated together to enable them to pass around 3D or5D bends, drive being provided by a common articulated drive shaft whichpasses through the tool.

FIG. 7 shows a tractor section 30 which may be used in such a tool. Thetractor section 30 incorporates a housing 32 provided with a turbine 34which is inductively coupled to a shaft within the housing 32.Furthermore a number of traction units 42 are mounted on the shaft byoffset rotary bearings (not shown) in a similar manner to the mountingof the cleaning units 8 and 28 and as more particularly described withreference to FIGS. 4b and 4 c of WO 98/06927. Each traction unit 42 ismounted on an annular bearing having its axis of rotation inclinedrelative to the shaft, and furthermore the mounting of the traction unitis offset forwardly or rearwardly relative to the centre line of thebearing.

Each traction unit 42, which is made of elastomeric material, has fiveoutwardly extending, equiangularly distributed legs 50 which areprevented from rotating with the shaft by cage members 51. The tractorsection 30 is fitted within the casing such that the legs 50 engage theinner wall of the casing so that, when the turbine 34 is rotated bymoving fluid, the rotating shaft drives the legs 50 of each tractionunit 42 such that each leg in turn is biased into engagement with thecasing wall and, whilst in contact with the wall, is moved in theopposite direction to the intended direction A of propulsion of thetool. The resulting reaction force tends to propel the tool in thedirection A, and each leg 50 is subsequently moved forwardly whilst outof contact with the casing wall, so that the combined effect of theswashing backwards and forwards motion of the legs 50 drives the toolcontinuously in the direction A. The direction of propulsion can bereversed by mounting the legs on the opposite side of the bearing centreline.

It might also be advantageous to mount the cleaning units 8 or 28forwardly of the bearing centre lines so that some degree of forwardbias is applied by the cleaning units to cause debris to be brushedback, as well as providing a degree of forward traction to assist inpropulsion of the tool. In this type of system it is not the intentionto use a catcher element for containing heavy debris, as the flow rateof fluid relative to the tool should be sufficient to carry the debrisback along the flow line to the rig or platform.

What is claimed is:
 1. Oilfield cleaning apparatus for cleaning theinner wall of an oilfield tubular, the apparatus comprising: a body tobe introduced into the tubular, the body being provided with at leastone cleaning element on at least one annular member such that a centralaxis of the at least one cleaning element is inclined relative to anaxis of rotation of the annular member, the body further having an axialfluid passage for the circulation of fluid to wash away debris dislodgedfrom the inner wall by the at least one cleaning element; and a drivemember acting to oscillate the at least one cleaning element in contactwith the inner wall of the tubular to scrape the inner wall with thecleaning element.
 2. The apparatus according to claim 1, wherein thedrive member acts to rotate the at least one cleaning element duringsuch osclllation.
 3. The apparatus according to claim 1, wherein theannular member is a rotary bearing member such that rotation of thebearing member causes the at least one cleaning element to be oscillatedaxially in contact with the inner wall as the bearing member is rotated.4. The apparatus according to claim 3, wherein the at least one cleaningelement is mounted on the bearing member such that the at least onecleaning element is offset from a centre line of the bearing member sothat the at least one cleaning element is biased towards and away fromthe inner wall as the bearing member is rotated.
 5. The apparatusaccording to claim 1, wherein the body is provided with a plurality ofcleaning elements disposed in an annular configuration.
 6. The apparatusaccording to claim 5, wherein the cleaning elements are separated bygaps for fluid flow.
 7. The apparatus according to claim 5, wherein thecleaning elements are provided on a plurality of annular members, whichare spaced apart axially along the body.
 8. The apparatus according toclaim 1, wherein the at least one cleaning element comprises outwardlyprojecting bristles or studs.
 9. The apparatus according to claim 1,wherein the at least one cleaning element has an outer surface which iscurved in the axial direction to assist contact with the inner wallduring oscillation of the cleaning element.
 10. The apparatus accordingto claim 1, wherein the at least one cleaning element is urged againstthe inner wall by the drive member such that the at least one cleaningelement is movable relatively freely in contact with the inner wall inone axial direction, but substantially less freely in contact with theinner wall in the opposite axial direction to provide the requiredscraping action.
 11. The apparatus according to claim 1, wherein acatcher element is mounted on the body for catching heavy debrisdislodged from the inner wall by the at least one cleaning element. 12.The apparatus according to claim 1, wherein the body comprises a lengthof pipe which is rotatable by the drive member in order to oscillate theat least one cleaning element.
 13. The apparatus according to claim 1,wherein an impeller member is mounted on the body and is drivable by thedrive member in order to direct heavy debris dislodged from the innerwall by the at least one cleaning element to a required containmentarea.
 14. The apparatus according to claim 1, wherein at least onejetting nozzle is provided on the body in the vicinity of the at leastone cleaning element to wash away debris dislodged from the inner wallby the at least one cleaning element.
 15. The apparatus according toclaim 1, wherein the drive means is adapted to impart drive to the atleast one cleaning element within a borehole from the surface by meansof a pipe string extending along the borehole.
 16. The apparatusaccording to claim 1, wherein the drive means incorporates a downholemotor for imparting drive to the at least one cleaning element within aborehole.
 17. The apparatus according to claim 1, wherein the drivemember comprises a fluid-driven member mounted on the body for impartingdrive to the at least one cleaning element within a borehole.
 18. Theapparatus according to claim 17, wherein the fluid-driven member is aturbine blade.
 19. The apparatus according to claim 17, wherein thedrive member incorporates at least one traction element for engaging theinner wall to impart a propulsion force for moving the body along thetubular when driven by the fluid-driven member.
 20. The apparatusaccording to claim 19, wherein the drive member is adapted to urge atleast a part of the at least one traction element outwardly against theinner wall whilst said part is moved relative to the body in theopposite direction to the direction in which the body is to bepropelled.
 21. The apparatus according to claim 19, wherein the at leastone traction element has a plurality of outwardly extending legssubstantially equiangularly distributed about a central axis, the drivemember acting to bias each of the legs in turn against the inner wall inoperation.
 22. The apparatus according to claim 19, wherein the at leastone traction element is mounted on a rotary bearing member which isinclined relative to its axis of rotation so as to cause the at leastone traction element to be moved alternately in opposite directions asthe bearing member is rotated.
 23. The apparatus according to claim 1,wherein a plurality of cleaning elements and traction elements aremounted on the body with at least one of the traction elements beingpositioned between two adjacent cleaning elements.
 24. The apparatusaccording to claim 1, comprising a plurality of cleaning modulesarticulated together to allow them to pass around bends, each cleaningmodule incorporating at least one cleaning element.
 25. A method ofcleaning the inner wall of an oilfield tubular, the method comprising:introducing into the tubular a body provided with at least one cleaningelement on at least one annular member such that a central axis of theat least one cleaning element is inclined relative to an axis ofrotation of the annular member so that the at least one cleaning elementcontacts the inner wall of the tubular; operating a drive to oscillatethe at least one cleaning element to scrape the inner wall with the atleast one cleaning element; and pumping fluid through an axial fluidpathway formed in the body to wash away debris dislodged from the innerwall.
 26. An apparatus for cleaning the inner wall of an oilfieldtubular, comprising: a body to be introduced into the tubular, the bodybeing provided with at least one cleaning element; drive means acting tooscillate the cleaning element in contact with the inner wall of thetubular to scrape the inner wall with the cleaning element; and acatcher element mounted on the body for catching heavy debris dislodgedfrom the inner wall by the at least one cleaning element.
 27. Theapparatus according to claim 26, wherein the catcher element is mountedon the body in such a way that the catcher element does not rotate inoperation to any substantial extent.
 28. The apparatus of claim 26further comprising an impeller member mounted on the body and drivableby the drive means in order to direct heavy debris dislodged from theinner wall by the at least one cleaning element to the catcher element.29. An apparatus for cleaning the inner wall of an oiltield tubular,comprising: a body to be introduced into the tubular, the body beingprovided with at least one cleaning element; and drive means acting tooscillate the cleaning element in contact with the inner wall of thetubular to scrape the inner wall with the cleaning element, wherein thedrive means comprises a fluid-driven member mounted on the body forimparting drive to the at least one cleaning element within a borehole,and wherein the fluid-driven member is a turbine blade.
 30. An apparatusfor cleaning the inner wall of an oilfield tubular, comprising: a bodyto be introduced into the tubular, the body being provided with at leastone cleaning element; drive member acting to oscillate the cleaningelement in contact with the inner wall of the tubular to scrape theinner wall with the cleaning element; and at least one traction elementhaving a plurality of outwardly extending legs for engaging the innerwall to impart a propulsion force for moving the body along the tubularwhen driven by a fluid-driven member.
 31. An oilfield cleaning apparatusfor cleaning the inner wall of an olifield tubular, the apparatuscomprising: a body to be introduced into the tubular, the body beingprovided with at least one cleaning element on at least one rotarybearing member such that a central axis of the at least one cleaningelement is inclined relative to an axis of rotation of the rotarybearing member, wherein the rotation of the rotary bearing member causesthe at least one cleaning element to be oscillated axially in contactwith the inner wall as the rotary bearing member is rotated; and a drivemember acting to oscillate the at least one cleaning element in contactwith the inner wall of the tubular to scrape the inner wall with thecleaning element.
 32. The apparatus according to claim 31, wherein theat least one cleaning element is mounted on the bearing member such thatthe at least one cleaning element is offset from a centre line of thebearing member so that the at least one cleaning element is biasedtowards and away from the inner wall as the bearing member is rotated.